
a ce sna aa 
Fic. 3.— Older 
seedling of Yucca 
angustifolia. 
BOTANICAL GAZETTE [JUNE 
November 23, 3:00 P.M.: growth 6™", mostly in zone 1; 
but curve of 90° mostly in zone 3, doubtless made before 
most of the growth in the root. 
In Yucca, as in Phoenix, the downward curve 
takes place in root or cotyledon, in whichever the 
most rapidly elongating part of the apical growing 
region falls. But the elongation of the more 
remote, parts of the cotyledon is not at first 
accompanied by any curve at all. Afterward, in 
the formation of the elbow, a combination of 
curves develops. These are in part probably 
geotropic, but are in part not under the direct 
influence of gravity, being executed in the develop- 
ment of structures whose initial position gravity 
determines. For the same reason as in the case 
of Cucurbita, a further treatment of these later 
curves is unnecessary here. 
The common statement is literally true, that 
these cotyledons are positively geotropic. But 
the meaning that has been conveyed by the words 
is only half correct. They do curve downward, 
but cannot perceive the gravity stimulus in a 
way that would make them curve so. As in the 
hypocotyl of Lupinus, any positive geotropism 
they may exhibit is under the control of the 
punctum vegetationis of the root, which alone is 
positively geoesthetic. 
WEST VIRGINIA UNIVERSITY. 
Morgantown, W. Va. 

